1. Field of the Invention
This invention is utilized for motor vehicle brakes, and for drum brakes in particular. It relates to a technique for reducing the so-called "brake noise" emitted when a motor vehicle brakes.
2. Description of Related Art
Much research has been carried out with the aim of reducing brake noise (the unpleasant "squeal" noise) produced when a motor vehicle brakes, and many proposals have been made regarding its reduction. The present applicant has been making a close study of this problem for a long time.
The technique disclosed in Jap. Unexamined Pat. No.3-288028 is a prior application by the present applicant and involves fitting a pressure member to the inside of the rim of the brake shoe by way of an intermediary friction member. The technique disclosed in Jap. Unexamined Pat. No.1-65944 is an older technique which is equivalent to the prior application of the present applicant, and involves fitting a friction member to the inside of the rim.
The technique disclosed in Jap. Unexamined Utility Model No.3-84436 likewise pertains to the prior application of the present applicant, and involves suppressing brake shoe vibration by fitting a weight to the inside of the rim. At the time at which this technique was disclosed, the idea of interposing an elastic member between the weight and the rim had not been thought of.
Subsequent experimental studies have confirmed the correctness of the analysis and explanation of brake noise given in the aforementioned Jap. Unexamined Pat. No.3-288028, and in particular the phenomenon explained with reference to FIG. 8 of the same publication. (This phenomenon will be explained in connection with the embodiments disclosed in the present application.) Namely, it has been found that the main cause of brake noise is vibration of the brake shoe, and that a brake shoe will vibrate in a radial direction as shown by the dotted lines in FIG. 27 of the application.
Brake noise is reduced by the aforementioned technique, and in the particular case of small passenger cars travelling on ordinary urban roads, it has been reduced to the level under which for practical purposes it is hardly a problem at all. However, under some conditions (and what these conditions are is not clear) the phenomenon of brake noise still occurs in the case of heavy duty vehicles, and further research is required to overcome this problem.
The present inventors have observed the phenomena associated with brake noise and have analyzed the results of these observations in a variety of ways. They have carried out experiments and analysis on vibration and have studied concrete measures for suppressing brake shoe vibration. The aforementioned experimental and analyses have involved new investigative methods, such as displaying vibration on a computer screen in an exaggerated form and correlating it with the frequency characteristics of the sound it produces. As the outcome of these studies, the present inventors propose the technique disclosed in this application. The experiments which they have performed have proven that this technique is far more useful than the previously known measures.